Lubrication systems in four cycle engines typically take one of two approaches, the first, a “wet oil sump” has a pool of oil at the bottom of the crankcase or oil pan together with an oil sump that siphons oil from the sump; or second, a “dry sump” which has an extra oil tank provided outside of the engine with an internal pump to distribute the oil to the engine. In either system, oil is distributed to lubricate such items as the main bearings of the crankshaft, the pistons and cylinder walls, connecting rods, cam shaft bearings, valves, and the like. In either the “wet sump” or “dry sump” system, oil is distributed through the various points and returned to the sump in a relatively closed loop system.
In the power sports industry, for example in four cycle engines that power snowmobiles and ATVs, the engines need to operate at extreme angles as the vehicles ascend and descend at a multitude of extreme angles. In this working environment, there has heretofore been tradeoffs between the wet oil sump and the dry oil sump methodology. As a dry sump system utilizes a closed volume for housing the lubricating oil, the volume of oil required to supply the system is less however the system is more complex as it requires an extra reservoir. The dry sump system however is less sensitive to the angles at which it operates and is therefore sometimes desired for extreme angles.
Wet oil sumps on the other hand, are easier to design as the engines are simply designed to allow the oil reservoir to pool at the bottom of the engine crankcase to create the oil sump. Due to the angle changes of the engine during the traversing of the vehicle, however, a larger volume of oil is required to ensure that the level of the oil is always maintained at or above the oil pump pickup.
Other shortcomings of present oil supply systems are also addressed in this disclosure. Most oil pumps are driven by a drive gear in meshing engagement with the crankshaft and the drive gear simply rotates within the pool of oil in the oil sump. This location of the drive gear within the oil sump may produce disadvantages to the overall system for a number of reasons. First, extra horsepower is required to drive the drive gear through the oil sump due to the resistance of the gear traveling in the oil. Second, the gear driven within the oil aerates the oil which in turn causes a decrease in the lubrication effect of the oil due to the air within the oil. Thirdly, driving the drive gear through the oil heats the oil which then in turn places a larger load on the oil cooler which may also cause an overall reduction in horse power.